1. Field of the Invention
The present invention relates to a lens barrel of an optical apparatus such as a camera.
2. Description of the Related Art
A camera is generally classified into a zoom camera enabling the change of the focal length of a photographic lens and a single focus camera whose focal length is fixed. Most of these cameras are provided with a lens barrel capable of protruding and retracting a photographic lens to downsize a camera when an image is not being captured (or when a power supply is turned off) and to enable to change focal length when an image is being captured (or when the power supply is turned on).
In recent years, there has been required a technique for reducing cost of these cameras while improving the functions thereof. This urges the development of a technique by which not only the cost for components is reduced, but also assembly workability is improved to reduce assembly man-hours and damaged products due to assembly error, thereby totally reducing the cost.
For example, in general, there exists a photographing apparatus such as a camera which is provided with a barrier mechanism for protecting the front face of a lens barrel from external dust. A technique has been proposed for facilitating an assembly workability in the barrier mechanism of this type. Japanese Laid-Open Patent Publication (Kokai) No. 05-27302, for example, discloses a prior art by which the barrier mechanisms are unitized to directly attach the unit to a lens holding member.
FIG. 11 is an exploded view showing the barrier unit in a prior art.
A barrier unit 110 is configured such that barrier blades 102 and 103, a drive ring 104, and springs 105, 106, and 107 are assembled with a base member 101, and attached to a lens barrel 109 incorporating a photographic lens (not shown). The drive ring 104 is rotated with respect to the base member 101 to open and close the barrier blades 102 and 103 using the urging force of the springs 105, 106, and 107.
A protrusion 104f extending in the direction parallel to an optical axis is formed on the drive ring 104 to open and close the barrier blades 102 and 103. Furthermore, a driving lever 108, engaged with the protrusion 104f to rotate the drive ring 104, is provided slidably in the direction of the optical axis on the inner surface of the lens barrel 109.
There has been known, as a technique for opening and closing the barrier of the barrier unit 110, a mechanism in which the protrusion 104f is provided on the drive ring 104 for opening and closing the barrier blades 102 and 103 and the driving lever 108 is caused to abut on the protrusion 104f to rotate the drive ring 104.
However, in the prior arts described above, when the open state of the barrier blades 102 and 103 is transformed to the closed state thereof, the direction of a force F20 applied to the driving lever 108 from the protrusion 104f is opposite to the direction of a force F10 applied when the barrier unit 110 is assembled. In other words, the direction of the force applied, when the barrier blades 102 and 103 are being closed, acts on the direction in which the barrier unit 110 is disassembled, so that the barrier unit 110 may easily drop out of the lens barrel 109. The problem cannot be sufficiently avoided even if a hooking mechanism such as a hook is provided on the barrier unit 110.
On the other hand, the problem can be avoided by firmly fixing the barrier unit 110 to the lens barrel 109 by means of screwing or gluing, however, in this case, the number of fixing components and the assembly man-hour increase and the gluing brings about damaged products. Thus, in this prior art, the assembly workability cannot be eventually simplified even if the barrier mechanisms are unitizeed, so that the total cost cannot be reduced in manufacturing a camera.